This application is a U.S. national phase application of International application PCT/JP98/04786 filed Oct. 22, 1998.
This invention relates to a brass material and a method of manufacturing the same, mainly relates to a brass pipe material and a method of manufacturing brass.
Previously, a brass pipe material generally comprises a single xcex1 phase material. This is a result of reducing a xcex2 phase ratio which inhibits cold ductility , providing for cold draw out (drawing) or cold bending fabrication.
However, a brass pipe material of a single xcex1 phase does not utilize a xcex2 phase excellent in machinability and polishability so that it has problems of inferior in machinability and polishability.
Also, the conventional brass pipe materials were made crystal grain diameter relatively large similarly to ensure cold ductility so that they have problems of inferior in corrosion resistance and strength.
An object of the present invention is to improve machinability and polishability in a brass material prepared through a cold working, particularly in a brass pipe material.
In the process of a brass material according to the present invention, a brass material excellent in machinability and polishability can be provided by increasing an area ratio of a crystal phase other than an xcex1-phase after extrusion or rolling.
As a suitable embodiment, when a composition comprises an apparent Zn content of 33.5 to 43% by wt., by heating to 550 to 800xc2x0 C., and when an apparent Zn content is 38.5 to 43% by wt., by heating to a temperature region of 550 to 800xc2x0 C., or 400 to 500xc2x0 C., the area ratio of a xcex2 phase can be increased, preferably the area ratio of a xcex2 phase can be made 5% or more.
Here, the term xe2x80x9can apparent Zn contentxe2x80x9d is used in the meaning of xe2x80x9c{(B+txc2x7Q)/(A+B+txc2x7Q)}xc3x97100xe2x80x9d wherein A is a Cu content [% by wt.], B is a Zn content [% by wt.], t is a Zn equivalent of the third element (e.g., Sn), and Q is a content of the third element [% by wt.].
For preventing decrease of the P phase once increased during cooling, when the temperature region to be heated is 550 to 800xc2x0 C., it is rapidly cooled at a cooling rate of 5xc2x0 C./sec or higher until 400xc2x0 C., and when the temperature region to be heated is 400 to 500xc2x0 C., it is rapidly cooled at a cooling rate of 1xc2x0 C./sec or higher until 400xc2x0 C.
As the other suitable embodiment, when an apparent Zn content is 33.5 to 43% by wt. and Sn content is 0.5 to 2.0% by wt., by heating to a temperature region of 400 to 500xc2x0 C., an area ratio of a xcex3 phase can be increased, preferably the area ratio of the xcex3 phase can be made 1% or more.
Here, when the temperature region of 400 to 500xc2x0 C. is maintained for one hour or more, the xcex3 phase becomes spherical so that strength or machinability and polishability are more improved. Also, for preventing decrease of the xcex3 phase once increased during cooling, it is preferably rapidly cooled at a cooling rate of 1xc2x0 C./sec or higher until 400xc2x0 C.
Incidentally, when an apparent Zn content is 33.5 to 43% by wt. and Sn content is 0.5 to 1.3% by wt., a cold working is easy since the Sn amount is relatively low, and in the case of the composition where an apparent Zn content is 33.5 to 43% by wt. and Sn content is 1.3 to 2.0% by wt., a xcex3 phase can be easily precipitated since the Sn amount is relatively large.
As the suitable embodiment in the present invention as mentioned above, a cold working such as bending processing or drawing processing of a pipe material can be carried out before a heat treatment step.
In this case, it is preferred that before the cold working, a heat treatment step for making an xcex1 phase to increase the area ratio of the xcex1 phase whereby cold ductility is previously secured. This heat treatment step for making an xcex1 phase is to maintain, for example, at 450 to 550xc2x0 C. for 10 minutes or longer when an apparent Zn content is 33.5 to 43% by wt. If a crystal grain size is coarsened during the heat treatment step for making an a phase, it can contribute to improve ductility at the time of the cold working.
And according to such a heat treatment step for making an xcex1 phase, before the cold working, the area ratio of the xcex1 phase can be made 90% or higher, preferably 95% or higher, or elongation in cold can be made 20% or higher, preferably 35% or higher.
Incidentally, after the cold working, an annealing step for controlling an internal stress is usually carried out. The timing of effecting the annealing step may be before or after the heat treatment step.
Also, in the method of production the brass material according to the present invention, by having a crystal grain size fining treatment during the heat treatment or in a step before the heat treatment, surface roughening at a bending processing can be reduced while further improving polishability by making the average crystal grain size of 50 xcexcm or smaller, preferably 25 xcexcm or smaller.
Such a crystal grain size fining treatment is desirably carried out after the cold working. That is, before the cold working, the crystal grain size is made relatively larger to ensure cold ductility, but when the crystal grain size is remained in a larger size after the cold working, polishability, corrosion resistance and strength become poor. Thus, by going through the crystal grain size fining treatment after the cold working, the crystal grain size can be certainly made small whereby the polishability, etc. are improved.
As a suitable embodiment, the crystal grain size fining treatment can be carried out by recrystallizing transformation introduced by the cold working under heating. In this case, it is desired to make a transformation density as high as possible at the cold working and a sectional area reduction ratio of 20% or more is preferred.
Also, in order to prevent the crystal grain size coarsen again, it is desired to set an upper limit in a heating time or to rapidly cooled after heating. For example, in a heat treatment heating to 550 to 800xc2x0 C., coarsening again of the crystal particle size can be prevented by making an upper limit of a heatingmaintaining time within 30 minutes.
As a suitable embodiment of the cold working in the present invention as mentioned above, when the cold working and annealing are carried out repeatedly, it is desired that an area reducing ratio at the final cold working is made large, and a temperature at the final annealing is made lower than the annealing during the procedure. For example, when the annealing temperature during the procedure is 500 to 600xc2x0 C., the annealing temperature at the final is desirably 500xc2x0 C. or lower.
Also, as a use of a process for producing a brass material according to the present invention, it is desirably applied to a method for producing a brass pipe material. This is because a pipe material is subjected to cold drawing and bending processing in many cases.
Subsequently, the brass material according to the present invention comprises satisfying at least one of (1) a machining resistance index based on, as the reference, the free-cutting brass bar conforming to JIS (Japanese Industrial Standard) C 3604 is 50 or higher,preferably 80 or higher, (2) through dezinking test conducted in accordance with the technical standard T-303 of JBMA (Japan Brass Makers Association ),corrosion resistance was confirmed as fellows: If the direction of maximum dezinking penetration depth is parallel with the working direction, the maximum dezinking penetration depth is not deeper than 100 xcexcm, and if the direction of the maximum dezinking penetration depth is rectangular to the working direction, the maximum dezinking penetration depth is not deeper than 70 xcexcm.
As a suitable embodiment of such a brass material, there is a pipe material, and it can be applied not only to the pipe material prepared by casting and extrusion after casting, but also to the pipe material (seam welded pipe, etc.) prepared by a plate material being subjected to bending fabrication, and then jointing the edge portion.
Incidentally, when this producing method is used, excellent characteristics can be shown with regard to the polishability in addition to the characteristics other than the mentioned above. That is, as for the polishability, it is evaluated in the view points that 1. when polishing is carried out in the same conditions, surface roughness after polishing is small as compared with the conventional material, 2. when polishing is carried out in the same conditions, a polishing amount is large as compared with the conventional material, and 3. when polishing is carried out in the same conditions, there is no defect in appearance and coverage of plating is good as compared with the conventional material. As a result of evaluation from these view points, the brass pipe material according to the present invention is shown to be excellent as compared with the conventional brass pipe material.
When the polishability is quantitated, in the pipe material according to the present invention, after the heat treatment, when a flaw of #80 is surface polished under the conditions of the polishing device of Viewler ECOMET IV, a polishing plate rotation number of 200 rpm, a sample pressing pressure of 6.9 KPa and a polishing paper of SiC #600, it has a characteristic of finishing the polishing within a time of xc2xd as compared with the brass pipe material according to Japanese Industrial Standard JIS C-2700.
Also, the pipe material according to the present invention, in the pipe material according to the present invention, after the heat treatment, when a flaw of #600 is surface polished under the conditions of the polishing device of Viewler ECOMET IV, a polishing plate rotation number of 150 rpm, a sample pressing pressure of 6.9 KPa and polishing powder of Al2O3, it has a characteristic of finishing the polishing within a time of xc2xd as compared with the brass pipe material according to Japanese Industrial Standard JIS C-2700.
As others, the pipe material according to the present invention has Sn as a starting composition and subjected to bending processing, and the portion in which the bending processing is carried out satisfies the maximum dezinking penetration depth of 70 xcexcm or less when the dezinking corrosion test is carried out according to Japanese Copper-Distend Association Technical Standard JBMA T-303 after the heat treatment.
Subsequently, the brass material produced by a cold working according to the present invention has a first phase comprising an xcex1 phase, and a second phase different from the first phase, and the area ratio of the first phase is 99% or less so that the machinability and polishability are improved as compared with the brass material prepared through the conventional cold working of an single xcex1 phase.
As a suitable embodiment, by making the area ratio of a xcex2 phase 5% or more, the machinability, etc. are to be ensured by effectively utilizing the xcex2 phase inherently excellent in the machinability and polishability. Moreover, by making the area ratio of the xcex2 phase 40% or less, preferably 20% or less, corrosion resistance can be ensured.
Further suitably, when an Sn concentration in the xcex2 phase is made 1.5% by wt. or more, improvement in corrosion resistance can be effected as a whole by strengthening the xcex2 phase which is inherently inferior in corrosion resistance.
Also, by making the average crystal grain size 50 xcexcm or smaller, preferably 25 xcexcm or smaller, not only inhibition of surface roughness at the bent portion and improvement in the polishability but also improvement in corrosion resistance and strength can be effected.
As the other suitable embodiment, by making the area ratio of a xcex3 phase 1% or more, strength is to be improved by utilizing strength possessed by the xcex3 phase while ensuring machinability, etc. by effectively utilizing the machinability and polishability at the intersurface between the hard xcex3 phase and the other phase. Suitably, by making the area ratio of the xcex3 phase 30% or less, brittleness possessed by the xcex3 phase is reduced.
More suitably, when the average crystal grain size (short diameter) of the xcex3 phase is made 8 xcexcm or smaller, preferably 5 xcexcm or smaller, brittleness possessed by the xcex3 phase is more reduced, but when an Sn concentration of the xcex3 phase is 8% by wt. or more, corrosion resistance is also improved. Particularly when the xcex2 phase is contained, by surrounding the xcex2 phase by the xcex3 phase with the Sn concentration of 8% by wt. or more, improvement in corrosion resistance can be effected as a whole by protecting the xcex2 phase which is inherently inferior in corrosion resistance.
The brass pipe material according to the present invention (including a raw tube which is not subjected to cold drawing) has the respective characteristic features of (1) the area ratio of the xcex3-phase is 1% or more, (2) it has a first phase comprising an xcex1-phase and a second phase different from the first phase, and the area ratio of the first phase is 99% or less and the average crystal grain size (short axis) of the above-mentioned second phase is 8 xcexcm or smaller, (3) it has a first phase comprising an xcex1 phase and a second phase different from the first phase, and the area ratio of the first phase is 95% or less and the average crystal grain size of 50 xcexcm or smaller, preferably 25 xcexcm or smaller, (4) the average crystal grain size is 25 xcexcm or smaller, the xcex1 phase is 25 xcexcm or smaller, the xcex2 phase is 20 xcexcm or smaller and the xcex3 phase is 8 xcexcm or smaller.
Similarly, the brass pipe material according to the present invention has the respective characteristic features of (1) machining resistance index based on , as the reference, the free-cutting brass bar conforming to JIS (Japanese Industrial Standard) C3604 is 50 or higher, preferably 80 or more, (2) when a flaw of #80 is surface polished under the conditions of the polishing device of Viewler ECOMET IV, a polishing plate rotation number of 200 rpm, a sample pressing pressure of 6.9 KPa and a polishing paper of SiC #600, it has a characteristic of finishing the polishing within a time of xc2xd as compared with the brass pipe material according to Japanese Industrial Standard JIS C-2700, (3) when a flaw of #600 is surface polished under the conditions of the polishing device of Viewler ECOMET IV, a polishing plate rotation number of 150 rpm, a sample pressing pressure of 6.9 KPa and polishing powder of Al2O3, it has a characteristic of finishing the polishing within a time of xc2xd as compared with the brass pipe material according to Japanese Industrial Standard JIS C-2700.
Subsequently, the brass pipe material according to the present invention has characteristic feature in that an apparent Zn content is 33.5 to 43.0% by wt. and Sn content is 0.5 to 1.3% by wt., or an apparent Zn content is 33.5 to 43.0% by wt. and Sn content is 1.3 to 2% by wt. As the other components, as for a Pb content, if it is too much, a cold ductility is lowered so that it is preferably 0.07% by wt. or less.
That is, if the apparent Zn content is too large, it is difficult to enlarge an xcex1 phase ratio at the time of cold working, and a xcex3 phase which inhibits the cold ductility at the annealing process for making the xcex1 phase is likely precipitated. While if the apparent Zn content is too small, it is difficult to enlarge a xcex2 and xcex3 phase ratio after the cold working so that it is made in the above range. According to this range, during the cold working, while ensuring the cold ductility, and after the cold working, the machinability and the polishability can be ensured.
Incidentally, in the former, an Sn amount is relatively small so that the cold working is easy, and in the latter, the Sn amount is relatively large so that the xcex2 and xcex3 phase can be easily precipitated.
In the brass pipe material according to the present invention as mentioned above, an apparent Zn amount is high as compared with the conventional brass pipe material so that at the time of hot extrusion, a ratio of the soft xcex2 phase is high and extrusion resistance becomes low whereby the extrusion property is excellent.
That is, if the extrusion is carried out at the same temperature region as the conventional brass pipe material, extrusion with an sectional area reducing ratio higher than the conventional one can be carried out and by subjecting to extrusion to the shape near to the final pipe shape, a load at the cold drawing thereafter can be reduced.
On the other hand, if the extrusion is carried out with an sectional area reducing ratio as the conventional one, extrusion at a temperature lower than the conventional one can be carried out so that a load for a billet heating can be reduced.
Here, after hot extrusion, it is desired to cool down as soon as possible. That is, Sn is added so that if a cooling rate after extrusion is slow, a xcex3 phase is precipitated with a large amount so that the latter heat treatment step for making an xcex1 phase takes a long time. Thus, when precipitation of the xcex3 phase is prevented by cooling as soon as possible and xcex1+xcex2 structure is made, a time necessary for the heat treatment step for making an xcex1 phase can be shortened.